FIGS. 1A and 1B respectively show two types of conventional sockets 10 and 12. The first type of socket 10 has a large diameter end 14 and a small diameter end 16. The second type of socket 12 has a unified outer diameter. Both the sockets have a cylindrical shape. When placing the socket on a ground, the socket tends to roll on the ground. (With respect to the socket 10, the heavier large diameter end 14 will roll on the ground, while the small diameter end 16 will not contact the ground. ) The cylindrical socket tends to linearly roll randomly, especially in the case that the ground is inclined or a worker kicks the socket. It often takes place that the socket rolls into a hidden corner or under a machine bed and is hard to recover. Especially in a large-size working site such as a repair work, the socket often rolls away unexpectedly and is lost. It leads to inconvenience in working.